        * {
            margin: 0;
            padding: 0;
        }
        
        * {
            box-sizing: border-box;
        }
        
        *::before {
            box-sizing: border-box;
        }
        
        *::after {
            box-sizing: border-box;
        }
        
        #demo {
            word-break: break-all;
        }
        
        #div1 {
            position: fixed;
            left: 50%;
            top: 20px;
            transform: translateX(-50%);
        }
        
        #div1::before {
            content: '';
            display: block;
            position: absolute;
        }
        
        #div1::after {
            content: '';
            display: block;
            position: absolute;
        }
        
        @media (max-width:500px) {
            #html {
                height: 50vh;
                overflow: auto;
            }
            #div1Wrapper {
                height: 50vh;
            }
            #div1 {
                position: relative;
                top: 0;
                right: 0;
            }
        }